1. Field of Use
This invention relates to improvements in the processability of elastomeric insulating materials that are asbestos free and especially suited for use as low smoke insulating in rocket motors. This invention, still more particularly, relates to improvements in the green properties of such elastomeric insulating materials that contain char forming organic fiber selected from polyaramide pulps as low density fillers which enhance the mechanical properties of the insulators and form a strong, adherent char upon cure and propellant burn.
Elastomeric insulating materials containing asbestos have long been employed within rocket motor cases including such portions thereof as their blast tubes. This invention relates to insulating materials which are similarly suited for use in rocket motors but are advantageously free of asbestos. U.S. Pat. No. 4,501,841 relates to elastomer formulations that have ingredients similar to those in the insulator formulations of this invention. However, the insulators specifically disclosed in U.S. Pat. No. 4,501,841 are difficult to process by calendaring or extrusion. Moreover, the green insulators specifically disclosed in U.S. Pat. No. 4,501,841 do not always have sufficient green strength for permitting them to be extruded or calendared optimally into ribbons that may be layed down with integral segments thereof tacking together in a manner such as disclosed in U.S. Ser. No. 378,588 filed May 17, 1982.
2. Objects of the Invention
It is an object of this invention to provide improved processability for low density, elastomer insulating materials useful in rocket motors.
It is an object of this invention to provide such elastomeric insulating materials in which certain char forming organic fiber replaces asbestos.
It is an object of this invention to provide such asbestos free elastomeric insulating materials that are low in smoke issuance and exhibit certain important properties as least as good as insulating materials containing asbestos.
It is an object of this invention to provide methods for compounding and use of these elastomeric insulating materials such that they may be readily calendered or extruded and yield green elastomeric material with desirable tack and physical properties.
These and other objects are achieved in accordance with practices of this invention; these practices are described more fully in the following together with the manner in which such objects are accomplished.
As used in the following description of this invention, the term "case wall insulation" refers to a layer or layers of material bonded to the internal wall of the rocket motor case to protect the case from the hot combustion processes occurring during the functioning of the rocket motor.
The term "blast tube insulation" in the following refers to material used to line the internal diameter of the blast tube of a rocket. The term "blast tube" refers to the conduit that conveys combustion products of the motor to the nozzle of the rocket. In some rocket motors, due to missile design, the nozzle cannot be connected directly to the rocket motor thereby requiring such a "blast tube." The blast tube lining protects this tube from the hot combustion gases of the rocket motor. "Blast tube ramp insulator" as used herein refers to the insulation material carried by an aftly converging section of a rocket motor between the rocket motor case (larger diameter) and the blast tube (smaller diameter). The term "low smoke" in reference to the elastomeric insulating materials of this invention means that firing of rockets in which these materials serve as insulation yields little or no smoke attributable to the insulations.
The nature of specific blast tube and blast tube ramp insulators, as well as case wall insulators, depends on both mass flux, in the area of application, and burning duration of the rocket motor.